One ubiquitous form of window treatment is the roller shade. A common window covering during the 19.sup.th century, a roller shade is simply a rectangular panel of fabric, or other material, that is attached to a cylindrical, rotating tube. The shade tube is mounted near the header of the window such that the shade rolls up upon itself as the shade tube rotates in one direction, and rolls down to cover the a desired portion of the window when the shade tube is rotated in the opposite direction.
A control system, mounted at one end of the shade tube, can secure the shade at one or more positions along the extent of its travel, regardless of the direction of rotation of the shade tube. Simple mechanical control systems include ratchet-and-pawl mechanisms, friction brakes, clutches, etc. To roll the shade up and down, and to position the shade at intermediate locations along its extend of travel, ratchet-and-pawl and friction brake mechanisms require the lower edge of the shade to be manipulated by the user, while clutch mechanisms include a control chain that is manipulated by the user.
Not surprisingly, motorization of the roller shade was accomplished, quite simply, by replacing the simple, mechanical control system with an electric motor that is directly coupled to the shade tube. The motor may be located inside or outside the shade tube, is fixed to the roller shade support and is connected to a simple switch, or, in more sophisticated applications, to a radio frequency (RF) or infrared (IR) transceiver, that controls the activation of the motor and the rotation of the shade tube.
Many known motorized roller shades provide power, such as 120 VAC, 220/230 VAC 50/60 Hz, etc., to the motor and control electronics from the facility in which the motorized roller shade is installed. Recently-developed battery-powered roller shades provide installation flexibility by removing the requirement to connect the motor and control electronics to facility power. The batteries for these roller shades are typically mounted within, above, or adjacent to the shade mounting bracket, headrail or fascia. Unfortunately, these battery-powered systems suffer from many drawbacks, including, for example, high levels of self-generated noise, inadequate battery life, inadequate or nonexistent counterbalancing capability, inadequate or nonexistent manual operation capability, inconvenient installation requirements, and the like.
Moreover, setting the operational range of a motorized shade or blind is necessary to assure control of solar gain and privacy. Therefore many known motorized roller shade designs have taken several approaches, for example, external limit switches, internal limit switches, and hard stops which stall the motor at the limits. Limit switches have inherent drawbacks as they can be expensive and can fail over time. External limit switches are typically installed during the installation which can be time consuming whereas internal limit switches are installed into the control system of the shade or blind and can be operated by lead screws and nuts or cams also adding cost. Hard stops require the installer to run a set up routine after the shade or blind is installed and provide a satisfactory way to set the upper and lower travel limits which define the operational range of the shade or blind. Typical drawbacks to hard stops include the noise, the wear and tear on the components and in the case of battery power supplies and the use of additional current to stall the motor which shorten the battery life.